Fix DefaultVersions.Generated.props syntax

[ViktorHofer]

Regressed with f684cee

We might want to think about in PR validation as that's the second case lately where CI passed but arcade-promotion then later failed.

To double check:

• The right tests are in and and the right validation has happened. Guidance: https://github.com/dotnet/arcade/tree/main/Documentation/Validation

[mmitche]

Gah! I did it again.

[riarenas]

It's worth noting that both of the breaks were caught by arcade-validation. I don't think there was a risk of promoting this break for repos that didn't take the updates manually.